Coolant being pushed back into expansion tank and then overflow - advice req

[vijilants]

Ok, here is the scenario - the coolant is being pushed back into the expansion tank and then out via the overflow.

Also noted was the continual clicking of the duovalves.

But the water in the expansion tank is not getting hot.

Could it be a) the thermostat

b) Head gasket

c) waterpump

d) Anything else ?


Your thoughts please ?

Many Thanks

 

[BTB 500]

If it happens when the coolant is cold then a leaking head gasket has got to be the prime suspect.

 

[LeighW]

I had the same symptoms on a previous car (not a merc), and it was head gasket failure.

 

[Will]

Head gasket failure is obviously a possibility, but also fairly rare in the way that you describe - I think the M111 engines do sometimes leak small amounts of oil etc out but not very often do they pressurise up the cooling system so badly that the expansion tank overflows?

Have you recently done any work on the cooling system? When was the coolant last topped up? If you don't top it up what level does it eventually settle down to?

How hot does the car run when up to temperature/stationary etc?

Will

 

[vijilants]

Thermostat replaces 6 months ago as it appeared to be sticking open.

Coolant hasn't been topped up in ages..the level has always been ok....just below the neck by the where the black part meets the transparent part....this car never looses water.

The problem has occured out of the blue.

Temp is running just below 100, which is within normal limits.

 

[television]

When the head gasket fails it gives the effect of boiling as the compression blows the water system up, also shown at its worse if you take the rad cap off

 

[vijilants]

The people that currently have the car are taking a long time to diagnose, and that concerns me, but I shouldn't be surprised really !!!

 

[Will]

Go on, who's looking at it?

 

[vijilants]

Will,

Check your PM

 

[Amrit]

Advise

Mate,

It happened to my car as well...I dont know if its best for Mercedees but I used Car Seal...I have done several miles and its safe & sound I am happy with product.....

 

[KLP 92]

Isn't this the typical sign of an airlock in the system? I think you need to check the basics before thinking about the worse case scenarios. Had the same issues with the SEC after changing the water pump, a new thermostat later and removing the airlock rectifed it.

If the water in the expansion tank is cold then your thermostat is non functional and not opening. Its the cheapest option, replace thermostat and recheck.

 

[vijilants]

Isn't this the typical sign of an airlock in the system? I think you need to check the basics before thinking about the worse case scenarios. Had the same issues with the SEC after changing the water pump, a new thermostat later and removing the airlock rectifed it.

If the water in the expansion tank is cold then your thermostat is non functional and not opening. Its the cheapest option, replace thermostat and recheck.

Hi Nav,

As per my post, my first though was thermostat. However, the car is not with me to diagnose.

However, can;'t really understand how it could airlock out of the blue. Cooling system has had no work on it for ages.

 

[rf065]

I had the same symptoms on a car years ago, the head was cracked.
Hope yours is something simpler and cheaper to fix.

Russ

 

[Mark300SL]

Run the engine up from stone cold for about 90 seconds then switch off
Remove expansion tank cap, if the system is poressurised then its almost certainly block/head/cooling system integrity.
The system doesnt get anything like hot enough to pressurise through normal channels, and that only leaves combustion pressures entering the cooling system.

I use this test a lot if I suspect a head gasket on one of my race engines. It cant tell you you don't have a head gasket issue but it can tell you that one exists.

Mark

 

[KLP 92]

Did you find out what the problem was?

 

[vijilants]

The Conclusion to the problem

Ok folks , this is what happened in brief:

1) MB had the car for two days and said it could be either the waterpump, radiator or even head-gasket !!! (Now that just about covers the whole cooling system - what rubbish)

2) I complained and told them that as far as I am concerned that this was schoolboy mechanics, and shouldn't be that difficult to diagnose - I wanted to make sure the guy was fully aware that I know how car engines work as I didn't want to hear a load of rubbish.

3) They then came back and said it was waterpump and also blocked rad - apparently no water circulating in the block.

4) I told them change the pump and leave the rad as I didn't believe that it was the rad - they refused saying that they have to change both.

5) A week later car was returned with new rad and waterpump - all OK now.

6) Warranty company refused to pay for the rad saying they don't cover blockage in the rad but it is covered for any other type of failure !!!! Waterpump was covered.

7) They also refused to pay the two hours diagnostics after initially agreeing - it actually took two days but nobody in the world would wear that so the diagnostic bill was two hours.

8) After writing letters of complaint I got the two hours out of them this week.

So thats it - The moral of this tale is read the small-print in the warranty and if you have the mechanical knowhow, check the car out yourself first.If you don't have that knowledge and send the car to the main dealer, you are at their mercy.

I could have very easily diagnosed this problem,and fixed it, but when it happened, it was Thursday 5pm. I needed a car for the following day and weekend, I knew I'd never get the required parts to fix it on the weekend , I had mobilo cover and warranty, so I thought i'd use them and save myself the agro.

I don't believe the rad was faulty and to be honest I should have asked for it back and had it tested, but I really don't have time for all of this at the moment.

So what did the total invoice read ?.....a few pennies short of £1000 !!!!

What a mistake that turned out to be

 

[television]

Sorry to hear that you got a bill like that and it must have made a hole in your budget, I wonder where it all going with things getting so expensive if they go wrong.

They could have slipped the water pump off and that would have told them all